OTTAWA — Federal lawyers are trying to block government witnesses from testifying before a military watchdog investigating the treatment of Taliban prisoners in Afghanistan, The Canadian Press has learned.

The Justice Department has invoked national security and told the Military Police Complaints Commission that subpoenaed witnesses will be allowed to appear at the inquiry, but they will be instructed to say nothing when hearings begin next month.

The position was laid out during a meeting among inquiry lawyers on Sept. 25, said the commission's lead attorney, Freya Kristjanson.

Critics say it is the latest attempt by the Conservative government to shut down the investigation into claims by human rights groups that the Canadian army knowingly handed over insurgents to torture in Afghan prisons.

The order effects "every single government employee" slated to come before the commission, including military officers and senior staff from both the Defence and Foreign Affairs departments.

Kristjanson said the inquiry, which begins Oct. 5 in Ottawa, could potentially be sidetracked for months by legal wrangling, with the refusal to testify being referred to Federal Court.

Sources close to the case say federal lawyers have cited a section of the Canada Evidence Act which allows the government to keep information secret if it's in the national interest.

Justice Department lawyers have offered to let the witnesses testify behind closed doors, as long as the commission writes out the questions ahead of time and is not present when the interviews take place.

The answers would be transcribed, censored for national security and handed to the commission.

All government witnesses have refused pre-inquiry interviews and federal lawyers filed motions on Tuesday hoping to quash commission subpoenas.

Lawyers representing both the commission, as well as complainants Amnesty International and the B.C. Civil Liberties Association, are aghast.

"I've never seen something like that in all of my life," said Kristjanson, who was counsel to the commission that investigated the Maher Arar deportation and torture case.

"It seems to me the government has never had any intention of co-operating."

Paul Champ, who represents both human rights groups, said the tactic is right in line with the government's game plan, which included a recent legal challenge that questioned the watchdog agency's jurisdiction to investigate the complaints.

In a judgment released last week, the Federal Court gave the Justice Department a partial victory by limiting the scope of the inquiry to the actions of military police officers in Kandahar.

A spokesman for Defence Minister Peter MacKay declined comment, as did military police and the Justice Department.

Reports that the prisoners -- handed over to the Afghans -- may have been tortured rocked the Conservative government in the spring of 2007.

They prompted Prime Minister Stephen Harper's government to sign a more stringent agreement with Afghan authorities, allowing Canadian diplomats to check on the status of transferred Taliban.

The government has repeatedly said it has found no credible evidence of abuse and only uncovered one case, in November 2007, of a prisoner being mistreated.

It has downplayed the allegations and at one point International Trade Minister Stockwell Day, who was in the public safety portfolio at the time, suggested that Taliban prisoners were trained to lie.

But the Justice Department has now confirmed to the commission for the first time that military police conducted "several" investigations in Kandahar into the alleged mistreatment of prisoners, but refused to discuss the conclusions.

It is well known that officers looked into allegations made by a University of Ottawa law professor that Canadian soldiers had mistreated prisoners in 2006. But the military's National Investigative Service has been silent about whether it formally probed claims made by Afghans.

Federal lawyers hinted last spring that they possess documents related to unspecified investigations, but they've never formally confirmed that Canadian military police investigated Afghan claims.

It is a significant and potentially explosive development.

Kristjanson said she suspected that investigations had been carried out and asked for copies of the reports almost a year ago. But she's now been told that the government has not had time to censor the reports and therefore won't provide them for the inquiry.

"The government has done everything it can to delay a meaningful hearing," she said. "It also indicates that despite public comments that it was co-operating, it has in fact not been co-operating."

New Democrat foreign affairs critic Paul Dewar said he cannot believe the lengths the government has gone to in order to sabotage the commission's investigation.

"All of this begs the question: What are they hiding?"